More than 30 unmarked graves are to be excavated at a Florida reform school where former students allege that children were routinely tortured and murdered by staff up to half a century ago.

Authorities are likely to find "crushed skulls and broken bones" in the graves, according to a group of men who claim that beatings and abuse were commonplace at the school in the 1950s and 60s, and that boys suddenly disappeared, victims of a brutal regime that was never held accountable for its crimes.

Charlie Crist, the state's governor, has stepped into the scandal by ordering an investigation into the allegations made by four former pupils of the Florida Reform School for Boys in Marianna, an institution set up in 1900 and using fear and harsh discipline to control delinquent students. He said he wanted to know if there were bones in the 32 shallow graves, which contain no names, dates or other details and have only crosses made of white metal piping to identify them.

"If there's an opportunity to find out exactly what happened there, to be able to verify if there were these kinds of horrible atrocities, we have a duty to do so," said Crist, who ordered the Florida Department of Law Enforcement to investigate. "Justice always cries out for a conclusion."

The allegations were made by four former students who call themselves the White House Boys, after the nickname of the school's punishment block. They went public after meeting on an internet blog and exchanging emails about their experiences, which they say included severe beatings and racial abuse.

"The staff were so brutal that even the slightest frown on your face, or the slightest word out of context, could cause you to be sent to the White House and be viciously beaten to the point that you would become unconscious and bleed profusely down your legs and back," Bryant Middleton, 63, said.

The men accept that the staff at the time are almost certainly dead but said it was important for the public to know what went on. The publicity prompted other former students to come forward.